This invention relates to the pouring of molten metal from a ladle or tundish into a receiving vessel, such as a mold of a continuous casting machine. It relates particularly to improvements in the construction of a molten metal slide gate valve commonly used to control the flow of molten metal from the bottom of a ladle or tundish.
Sliding gate valves for molten metal are generally comprised of stationary upper and lower refractory plates each having a sized molten metal orifice and a reciprocable refractory slide plate in between the upper and lower plates. The reciprocable slide plate also has a sized molten metal orifice which, as the slide plate is reciprocated, moves in and out of registry with the molten metal orifices in the top and bottom plates to either open or close the valve to the flow of molten metal. A discharge nozzle is usually mounted below the lower stationary plate in alignment with the lower plate molten metal orifice to direct the stream of molten metal into a mold or other vessel. The refractory plates are all mounted in a steel frame attached to the bottom of the ladle or tundish and a hydraulic or pneumatic cylinder is used to reciprocate the middle slide plate.
While the refractory plates are held tightly together in the steel frame with springs, it has been noted that air is still capable of being drawn into the molten metal orifices in the plates which causes oxidation of the molten metal as it is being discharged through the sliding gate valve. If the molten metal is aluminum-killed steel, the aluminum in the steel will be oxidized forming particles of alumina which adhere to the discharge nozzle or remain in the steel as harmful inclusions.
Past attempts to prevent the infiltration of air into the sliding gate valve or by flooding the area around the plates have not been successful in preventing the infiltration of air into the plate orifices.